This application claims Paris Convention priority of DE 200 18 805.4 filed Nov. 3, 2000 the complete disclosure of which is hereby incorporated by reference.
The invention concerns a grinding machine having a stationary wall part and a plate part, which can rotate about an axis of rotation, wherein a gap is formed between the stationary wall part and the plate part.
A grinding machine of this type is disclosed in DE 196 06 117 A1. Such a grinding machine operates under the influence of centrifugal force. Workpieces to be treated and grinding material are disposed within the inner space formed by the wall and the plate part, and rotated through rotation of the plate part to effect a polishing effect through the influence of centrifugal forces and the relative speeds between the workpieces and grains of grinding material.
In a known embodiment, the annular gap between the rotary plate part and the stationary wall part is limited from the upper side by an elastic lining of the wall part, and, on the lower side, by a ceramic ring disposed on the rotary plate. The ceramic ring has a rectangular cross-section. The plate part is formed directly below the ceramic ring and tapers inwardly towards the bottom. While the elastic lining, due to its elasticity, is hardly worn by the grinding material bodies, it has turned out that the ceramic ring experiences large wear as a result of continuous exposure to grinding bodies, wherein, in particular, grinding material bodies collect in the gap and, through their abrasive effect, grind down the ceramic ring in the region of its inner upper edge thereby forming a step having a depth of 3 mm to 5 mm, within a short period of time. Grinding material can collect therein and accumulates up to the lower edge of the lining of the stationary wall to cause further wear of the ceramic part in response to the relative motion between the wall and the plate parts. The ceramic part must therefore be replaced after a short period of time.
It is the underlying purpose of the present invention to further develop a grinding machine of the above-mentioned type which has a longer service life.
This object is achieved in accordance with the invention by a grinding machine of the above-mentioned type, characterized in that the gap is limited from the top by a ceramic part and from the bottom by an elastic part. It has surprisingly turned out that, compared to prior art, the abrasive effect of the grinding material bodies on the ceramic part is much less if the ceramic part is disposed on the lower side of the stationary wall, wherein the ceramic ring limits the gap from above. The gap is limited from below by the elastic lining of the rotary plate part. The reason for the reduced wear may be that, although a small step also forms in the region of the inner lower edge of the ceramic ring due to the abrasive effect of the grinding material bodies, grinding material cannot collect and accumulate therein, since it is constantly removed by the undamaged opposite edge of the elastic lining of the plate part.
The invention therefore provides for a much longer service life compared to prior art. The ceramic ring must only be replaced after a much longer period of use.
The elastic part of the plate part is preferably a lining thereof while the ceramic part is a ceramic ring. Preferably, surfaces are provided between the two opposite planes which are preferably oriented horizontally and perpendicularly with respect to the axis of rotation. They can also incline slightly towards the inside with respect to the horizontal, e.g. in a range of 10xc2x0 to 30xc2x0. The axis of the grinding machine is usually vertical. A particularly preferred embodiment of the invention is characterized in that the ceramic part has a nose-like projection extending downwardly, wherein, in particular, the inner wall of the plate part and wall part are formed substantially conically, tapering from the top towards the bottom above and below the gap. The conical inclination of the inner wall with respect to the vertical axis of rotation can thereby be 30xc2x0 to 45xc2x0. Both, this inclination of the plate part directly below the gap as well as the conical inclination extending inwardly and downwardly of the inner wall of the wall part, support the abrasion-preventing arrangement of the gap-limiting ceramic part on the upper wall part and the elastic part of the rotary plate limiting the lower side of the gap.
Further advantages and features of the invention can be extracted from the claims and the following description which show, in detail, an embodiment of the invention with reference to the drawing.